How to use H.248.26 package xal/las together with amet/em

Hello,
Could you please tell us whether our understanding of xal/las is right?

In our scenario, MGC send "SG{xal/las}" to calling side to indicate that the called side answer the call and local charging should start.

During the call is ongoing, MGC send "SG{amet/em}" for the charging pulse purpose, but the signal "xal/las" is not included.

According H248.1, however, "a new signal should replace the former signal on MG", so the calling side MG will replace "xal/las" with signal "amet/em", so MG lost signal "xal/las" and it indicates that called side onhook the call and the charging finished.

It is right?

Thanks a lot.

Best Regards,
Xu Jian